The present invention generally relates to quantum effect semiconductor devices, and more particularly to a quantum effect semiconductor device having a one-dimensional ultra-fine wire structure for confining carriers.
Recently, there is active research in the field of one-dimensional ultra-fine wire structure (hereinafter referred to as a quantum well wire) for confining carriers. When the quantum well wire is used as a channel of a quantum effect semiconductor device, the impurity scattering decreases at low temperatures. Accordingly, the mobility of the carriers increases, thereby increasing the switching speed of the quantum effect semiconductor device. This technology is also important when forming a quantum well box.
FIG. 1 is a perspective view of an essential part of a quantum effect semiconductor device proposed in "Scattering Suppression and High-Mobility Effect of Size-Quantized Electrons in Ultrafine Semiconductor Wire Structures" by H. Sakaki, Japanese Journal of Applied Physics, Vol.19, No.12, December 1980, pp.L735-738. In FIG. 1, the semiconductor device comprises a barrier layer 1, a channel layer 2, a barrier layer 3, an insulator layer 4, a gate electrode 5, and a channel region 6.
FIG. 2 is a perspective view of an essential part of a quantum effect semiconductor device proposed in "One-Dimensional Localization and Interaction Effects in Narrow (0.1 .mu.m) Silicon Inversion Layers" by W. J. Skocpol et al, Physical Review Letters, Vol.49, No.13, 27 Sept. 1982. In FIG. 2, the semiconductor device comprises a p-type silicon (Si) substrate 11, a channel layer 12, an insulator layer 13, and a gate electrode 14.
FIG. 3 is a perspective view of an essential part of a quantum effect semiconductor device proposed in "Toward Quantum Well Wires: Fabrication and Optical Properties" by P. M. Petroff et al, Applied Physics Letters, 41(7), 1 Oct. 1982. The semiconductor device comprises a barrier layer 21, a channel layer 22, a barrier layer 23, and a barrier layer 24.
In each of the proposed semiconductor devices shown in FIGS. 1 through 3, the channel layer constitutes a quantum well wire.
On the other hand, "Semiconductor Quantum-Well Structures for Optoelectronics; Recent Advances and Future Prospects" by H. Okamoto, Japanese Journal of Applied Physics, Vol.26, No.3, March 1987, pp.315-330 discloses a method of forming the quantum well wire by focused ion beam (FIB) injection of gallium (Ga) ions.
However, according to these proposed methods, it is thought extremely difficult to actually realize a quantum effect semiconductor device having the quantum well wire for the following reasons.
Firstly, according to the proposed semiconductor device shown in FIG. 1, a V-groove having a V-shape is formed in the barrier layer 1, the channel layer 2 and the barrier layer 3, and the insulator layer 4 and the gate electrode 5 are then formed in the V-groove. It is impossible to obtain a satisfactory characteristic for the semiconductor device because the channel layer 6 is formed at a processed surface which is processed at the time of forming the V-groove, and furthermore, since the insulator layer 4 is formed on the channel layer 6 after the formation of the V-groove. In other words, an interface between the channel layer 6 and the insulator layer 4 is subjected to two processes, that is, the process of forming the V-groove and the process of forming the insulator layer 4. This means that the channel layer 6 is extremely close to the processed surface of the V-groove and is also easily damaged during the process of forming the insulator layer 4.
Secondly, according to the proposed semiconductor device shown in FIG. 2, the width of the quantum well wire is only 0.1 .mu.m and is not sufficiently small to obtain a satisfactory one-dimensional quantum effect.
Thirdly, according to the proposed semiconductor device shown in FIG. 3, the channel layer 22 is formed at a processed surface as in the case of the device shown in FIG. 1, and it is impossible to obtain a satisfactory characteristic for the semiconductor device.
Fourthly, according to the method of forming the quantum well wire by the FIB of Ga ions, the width of the quantum well wire which can be formed is in the order of 0.1 .mu.m and is not sufficiently small to obtain a satisfactory one-dimensional quantum effect.
The problems of the conventional semiconductor device having the quantum well wire can be summarized as follows. That is, it is extremely difficult to obtain such a quantum well wire that displays a notable quantum effect or confines the carriers one-dimensionally, because the channel is formed at a processed surface and the processing technique is not yet established for forming a quantum well wire.